Propagation/Greenhouse Management
Part 1 – 124 | Unit 1.3
b) Kelp extracts and powders supply micronutrients, naturally occurring growth hormones,
a minor amount of N and up to 4%K, all in a form readily accessible to crops. Care should
be taken using kelp meal extracts in seedling mediums, as too much can stunt plant
growth.
c) Worm castings tea (dilute N-P-K and disease suppression)
d) Compost teas, brewed on farm from high quality composts can provide a dilute source
of N-P-K and micronutrients. By inoculating soil and foliage with beneficial bacteria and
fungi, they can also suppress diseases.
e) As the market for inputs has expanded, a wide array of soluble products has become
available. Growers should consult with others in their area to see what products have
been most valuable and provide the greatest return on investment.
E. Container Formats for Seedling Production (see Appendix 6, Examples of Propagation Containers)
- Cell/plug type trays: The most common containers for contemporary seedling production.
They are manufactured in a huge array of cell sizes and cell shapes. The key is to match
cell size with root nature of the crop, size of desired transplant, appropriate media, and
available space in the greenhouse. These containers are normally made out of expanded
polystyrene, high density polypropylene ,or polyethylene. Each has advantages and
disadvantages.
a) Advantages of cell/plug trays
i. The close spacing of cells allows growers to maximize plant density in valuable
greenhouse space
ii. Because cell size are relatively small when compared to traditional wooden flat-
grown crops, growers use very little soil media to produce thousands of plants
iii. Because each plant grows individually, in a separate cell, roots do not intertwine and
thus do not have to be separated at time of transplanting
iv. Roots are “air pruned” when they reach the bottom of the cell, in most plug tray
designs, which causes roots to branch higher up and more rapidly fill out the root
ball
v. Because plants with well “knitted” roots that hold the soil ball together can be easily
removed from the plug trays, it is possible to plant most crops with little to no
transplant shock, assuming the grower otherwise uses good transplanting practices
b) Disadvantages of cell/plug trays
i. The small volume of soil used cells/plugs means that each individual plant has
limited access to soil nutrients, thus increasing the likelihood growers will have to use
supplemental fertility to keep plants growing strong or to hold them if transplanting
time is delayed
ii. Small cells have limited root runs, which shortens the window of opportunity for
optimal transplant timing, again leading to the potential need for supplemental
fertility
iii. The small volume of soil means that growers will have to water more frequently to
compensate for the rapid soil drying that is likely when temperatures are hot and
plug sizes are small
iv. Some flat bottom cell designs drain poorly and actually hold water at the bottom
of the cell. This “perched water table” can be problematic for crop roots sensitive to
rotting or those needing abundant oxygen throughout the root zone.
v. Some round cell designs can promote “root spiraling,” causing plants to become root
bound early in their development
Lecture 4: Soil Media, Fertility, & Container Formats